Hydro-turbine runner

ABSTRACT

A turbine disposed in a water passageway includes a hub and associated runner blades. Each blade comprises an inner edge and a distal outer edge, a leading edge and a trailing edge separated by a water directing surface. Each blade is rotatable relative to the hub about a blade rotational axis. The water passageway includes a spherically-shaped discharge ring that conforms to the outer edges of the blades to improve certain turbine parameters such as cavitation, efficiency, flow disturbance, and fish survivability. The turbine hub may also include a spherically-shaped outer surface in a region swept by the inner edges of the blades when the blades are rotated from maximum to minimum pitch, as well as seals attached to the inner edges of the blades. The hub may also be associated with blades in which the chord is reduced in the root region of the blade.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.08/800,240, filed Feb. 12, 1997, now U.S. Pat. No. 5,954,474 which is acontinuation-in-part of U.S. patent application Ser. No. 08/623,245 nowU.S. Pat. No. 5,947,679, filed Mar. 28, 1996.

FIELD OF THE INVENTION

The present invention relates generally to hydroelectric turbineinstallations. More particularly, this invention pertains tohydroelectric installations utilizing propeller-type turbines in whichthe angular position of the runner blades relative to the hub of theturbine or propeller, i.e. the pitch of the blades, is adjustable.

BACKGROUND OF THE INVENTION

Hydroelectric turbine installations in which the turbine comprisesseveral runner blades having an adjustable pitch are widely used. Inthese turbines, each runner blade (often simply called a “blade”), ispivotally connected to the hub having a longitudinal axis, the bladestypically including a trunnion which is rotatable about an axisextending in a direction generally perpendicular to the hub. Therotation of each blade about its axis permits the turbine operator tovary the amount of power produced and seek the optimum efficiency of thehydroelectric installation under the entire range of operatingconditions of the turbine.

In the hydroelectric industry, the most common type of turbine withadjustable pitch blades is referred to as a “Kaplan” turbine in whichthe axis of rotation of the blades is substantially perpendicular to thehub longitudinal axis. In relatively few instances where this conditionis not met, the turbine is called a “Deriaz” turbine. However, tofacilitate the reading of this application, in the following we willsimply discuss the present invention in connection with Kaplan turbinesbecause the principles of operation and operating parameters of Deriazturbines that are of interest to the invention are substantially thesame as those of Kaplan machines.

Kaplan turbines are also typically provided with adjustable wicket gatesdesigned to regulate the flow of water admitted to the turbine.Accordingly, for each point of operation of such a turbine there is anoptimum gate opening and blade opening condition that maximizes poweroutput for the amount of flow passing through the turbine.

It is well recognized that hydroelectric power generation is generallysocially more desirable than its counterparts which obtain energy fromthe combustion of fossil fuel or the fission or fusion of atoms. It isalso widely accepted that Kaplan turbines materially improve theefficiency of hydroelectric installations. However, it is increasinglybeing suspected that certain Kaplan installations have variousdetrimental impacts on the environment, particularly on the fishpopulation which is present in the water flowing through the turbine.

One of these potentially adverse impacts results from the very featuresof Kaplan turbines that increase the efficiency of hydroelectricinstallations using these turbines, namely the adjustable blades.Specifically, in a Kaplan turbine having its main axis generallyparallel to the direction of the flow of water passing through theturbine, the pitch of the blades is adjustable from maximum to minimumblade opening or pitch, the blade forming a greater impediment to theflow of water when it is in the minimum pitch position (i.e., when theface of each blade is substantially perpendicular to the water flow).

Prior art Kaplan turbines are commonly provided with a frusto-sphericalhub, i.e., in which the portion of the hub extending between twoparallel planes passing through the intersection of the radiating linesR and the hub, is spherically-shaped as illustrated in FIGS. 2-5. Inother words, and as more particularly shown in FIGS. 2 and 4, in suchKaplan turbines the surface region of the hub swept by the blades as theblades are moved between maximum and minimum pitch is not fullyspherical. In that case, the blade inner surface conforms to the shapeof the hub when the blade is at maximum pitch. However, gaps (oftenwedgeshaped) form between the blade inner surface and the hub surface asthe blade departs from the maximum pitch position. A similar situationoccurs in cases where the blade inner surface extends beyond thesubstantially spherical portion of the hub falling between the linesradiating from the hub center. Consequently, in both of these cases thesurfaces of each blade facing the hub (i.e., the inner surface of eachblade) do not fully conform to the outer surface of the hub over theentire range of blade positions. This means that as the blade departsfrom maximum pitch position (e.g., moving from position 5B to position5A), a gap is formed between the hub and the blade edge, as moreparticularly illustrated in FIGS. 3 and 5.

Various studies have shown that gaps formed between the blades and thehub of a Kaplan turbine have several detrimental effects. First, such“detrimental” gaps (which are not to be confused with the functionalclearances established between relatively movable part, such as forexample clearance δ shown in FIG. 9A existing between the hub outersurface and the inner surface of the blade for suitable movement of theblades relative to the hub) formed between the hub and certain regionsof the blades cause efficiency losses. This is because water leakingthrough such gaps typically lessens the ability of the blades to extractenergy from the flow of water passing through the turbine. As can bereadily appreciated, runner blades are configured so that waterimpinging thereon causes rotation of the runner to transform rotation ofthe runner into electrical energy. Water leaking through a gap thereforereduces the amount of water available to generate electrical energy,thereby reducing the efficiency of the turbine installation.

Furthermore, water leakage through a gap results in high turbulence andmay also cause a phenomenon known as cavitation. As is well known in theart, cavitation occurs when components of the water flow move intoregions of relatively low static pressures in the flow of water.Cavitation manifests itself by the production of bubbles of water vaporin low pressure regions of the water flow. When these bubbles of watervapor enter regions of higher pressure, they implode thereby causingdamage (in the long run) to nearby structures such as the runner blades.As is well understood by those skilled in the art, a gap between the hubsurface and the blade typically promotes cavitation. This is because thegap puts the high pressure side of the blade in fluid communication withits low pressure side (i.e., the suction side), potentially creatingintense vortices which cause an undesirable cavitation condition.

In addition to efficiency losses and cavitation problems, gaps also forma trap for fish which are present in the water flowing through theturbine. It is believed that fish flowing into such gaps have asignificantly greater chance of being injured or killed than fishflowing through other regions of the turbine. Recent efforts havetherefore been undertaken to address the apparent propensity of Kaplanturbines to injure fish.

In particular, systems have been designed to divert fish away fromKaplan turbines. These systems include screens to keep fish out of theturbine, or structures configured to divert fish away from the turbine.It can be readily appreciated, however, that these prior art structureshave several shortcomings. First, systems of the type necessitatingseparate structures consume some of the water normally flowing throughthe turbine thereby reducing the energy produced by the turbineinstallation. Second, it has been found that these systems are not fullyeffective to divert the entire fish population away from the turbine andmay cause mortality to the fish. In addition, screens disturb the waterflow and cause efficiency losses within the turbine. Finally, as can bereadily appreciated, these additional structures, which in addition tonot being entirely satisfactory, materially increase the cost ofhydroelectric installations using Kaplan turbines.

Generally, various attempts have also been made to increase theefficiency of adjustable pitch propellers and turbines by reducing thegap formed in these mechanisms. For example, U.S. Pat. No. 2,498,072issued Feb. 21, 1950 to Dean discloses an aircraft propeller in whichthe pitch of the blades is adjustable. To reduce air turbulence and dragin the region of the gap formed at the base of the blade, a seal made ofmolded rubber is attached to the hub embracing the blade airfoil.

More specifically, other attempts have been made to optimize theefficiency/cavitation ratio of Kaplan turbines and of hydroelectricturbines of other types. For example, U.S. Pat. No. 5,226,804 issuedJul. 13, 1993 to Do discloses a propeller-type runner in which theblades are fixed in position relative to the hub. The leading edge ofeach of the blades includes an enlarged forward region projecting towardthe trailing edge of the immediately preceding blade. As noted in Do, ithas been found that such a blade configuration reduces cavitation andproduces superior torque.

Still another example of an approach used to improve the operatingcharacteristics of certain rotating bladed implements is found in airfans, and in particular in axial flow fans having adjustable blades asdisclosed in U.S. Pat. No. 2,382,535 issued on Aug. 14, 1945 to Bauer.In Bauer, to improve the efficiency of the fan, the fan is provided witha substantially spherically-shaped wheel periphery and a annular recessformed opposite the tip of the blades. The close tolerance between thewheel and the blades and the blades and the recess generally improvesthe efficiency of the fan.

The foregoing indicates that various attempts have been made to increasethe efficiency of air propellers, fans, and Kaplan turbines. However, inview of the diverse detrimental effects resulting from the formation ofgaps between the blades and hub or the blades and passageway of Kaplanturbine, it seems desirable to provide effective ways to reduce the sizeof these gaps and thereby improve certain operating characteristics ofKaplan turbines without materially impairing others.

SUMMARY OF THE INVENTION

The present invention reduces the detrimental effects of gaps normallyformed between the hub and blades of Kaplan turbines, particularlyimproving the survivability of fish present in water flowing through aturbine, reducing cavitation and turbulent leakage flow, and otherwisegenerally improving the efficiency of such turbines.

A turbine in accordance with one aspect of the present inventioncomprises a hub and associated blades. The angular position of eachblade relative to the hub (i.e., the pitch of each blade) is adjustable.The turbine is situated in a water passageway comprising a dischargering having a face substantially facing the outer edges of the turbineblades. At least a portion of the face of the discharge ring isspherically shaped so that the outer edges of the blades conform withthe spherically shaped portion of the ring as the blades rotate betweenmaximum pitch and minimum pitch positions to reduce outer gaps formedtherebetween. The hub also includes a spherically shaped portion so thatthe inner surface of each blade oppositely facing the hub substantiallyconforms to the outer surface of the spherical portion of the hub toreduce inner gaps formed therebetween. The inner and outer gaps arepreferably reduced such that only the necessary functional clearance isformed between the inner and outer blade surfaces and the hub anddischarge ring surfaces over the entire range of blade positions (i.e.,from maximum to minimum pitch).

According to other aspects of the invention, the turbine installationmay include additional features configured to further reduce the innerand outer gaps or reduce gaps formed in other areas of the installation.

Other advantages of the invention will become apparent from the detaileddescription given hereinafter. It should be understood, however, thatthe detailed description and specific embodiments are given by way ofillustration only since, from this detailed description, various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred exemplary embodiment of the invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements and:

FIG. 1 is an elevational view, partially in cross section, of ahydroelectric installation including a turbine with adjustable blades;

FIG. 2 is a partial schematic side elevational view of a Prior Artturbine runner;

FIG. 3 is a schematic top plan view of the Prior Art turbine runner ofFIG. 2, the adjustable blade shown at minimum pitch position;

FIG. 4 is a partial schematic front elevational view of the Prior Artturbine runner of FIG. 2 showing two blade positions;

FIG. 5A is a partial schematic cross sectional view taken along line5A—5A shown in FIG. 4, illustrating a gap formed between the blade andthe hub (in the leading and trailing edge regions of the blade) at lessthan maximum pitch position of the blade;

FIG. 5B is a partial schematic cross sectional view taken along line5B—5B shown in FIG. 4, illustrating the reduced gap region between theblade and the hub (in the leading and trailing edge regions of theblade) at maximum pitch position of the blade;

FIG. 6 is a side elevational view of a first embodiment of the hub andone associated blade in accordance with the present invention, the bladebeing shown at maximum pitch position;

FIG. 7 is a front elevational view of the first embodiment shown in FIG.6, the blade being shown at minimum pitch position;

FIG. 8 is a front elevational view of the first embodiment shown in FIG.6, the blade being shown at maximum pitch position;

FIG. 9A is a partial schematic cross sectional view taken along line9A—9A shown in FIG. 7, illustrating that, at less than maximum pitchposition of the blade, the gap formed between the blade and the hub inthe leading and trailing edge regions of the blade is limited to afunctional clearance;

FIG. 9B is a partial schematic cross sectional view taken along line9B—9B shown in FIG. 7, illustrating that, at maximum pitch position ofthe blade, the gap formed between the blade and the hub in the leadingand trailing edge regions of the blade is also limited to a functionalclearance;

FIG. 10 is an enlarged partial cross-sectional view of a portion of theleading edge of the blade taken along line 10—10 shown in FIG. 6;

FIG. 11 is a top plan view of a blade of the present invention showingthe spherically-shaped inner surface of the blade;

FIG. 12 is a front elevational view of the hub and one associated bladein accordance with another embodiment of the present invention, showinga seal attached to the inner surface of the blade;

FIG. 13 is an enlarged side elevational view of the blade of FIG. 12viewed from the inner surface end thereof, illustrating the sealattached thereto;

FIG. 14 is an enlarged partial cross sectional view taken along line14—14 of FIG. 13, showing a first configuration of the blade seal;

FIG. 15 is an enlarged partial cross sectional view taken along line14—14 of FIG. 13, showing a first modified configuration of the bladeseal;

FIG. 16 is an enlarged partial cross sectional view taken along line14—14 of FIG. 13, showing a second modified configuration of the bladeseal;

FIG. 16A is an enlarged partial cross sectional view taken along line14—14 of FIG. 13, showing a third modified configuration of the bladeseal;

FIG. 17 is a partial front elevational view of the hub and blades inaccordance with the present invention, the discharge ring regions of theturbine being shown in partial sectional view, illustrating the outersurfaces of the blades conforming to a spherically-shaped dischargering;

FIG. 18 is a partial sectional view along one of the blades rotationalaxis of a spherically-shaped hub in accordance with another embodimentof the present invention, showing the angled linkage connecting theblades to the blade positioning mechanism;

FIG. 19A is a partial sectional view of the spherically-shaped hub andangled linkage taken along line 19A—19A of FIG. 18;

FIG. 19B is a partial sectional view of the spherically-shaped hub andlinkage mechanism taken along line 19B—19B of FIG. 18;

FIG. 20 is an enlarged partial sectional view of a portion of the angledlinkage taken along line 20—20 of FIG. 18;

FIG. 21 is a graphical comparison between the normalized chordaldistribution of a blade in accordance with another embodiment of thepresent and that of a prior art blade; and

FIG. 22 is a graphical illustration of the variation of the clearancegap formed between the blade outer surface and the face of a dischargering configured in accordance with a further aspect of the present.

DETAILED DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT

The present invention relates generally to hydroelectric installationshaving turbines provided with features designed to reduce gaps formedbetween the hub and associated blades, and between the blade outersurfaces or tips and the discharge ring. Such features are configured toimprove the survivability of fish present in water flowing through theturbines, reduce cavitation and flow disturbance, improve the efficiencyof the turbine, or otherwise enhance the operation of the installation.The turbines are of the Kaplan-type in which several blades pivotallyare connected to the hub. It should be understood, however, that theinvention is applicable to any other type of turbine or propeller inwhich the blades are pivotally adjustable with respect to the hub.

Referring to FIG. 1, a hydroelectric turbine installation generallydesignated as 10 comprises a passageway 12, in which water flows from anupper elevation source in fluid communication with the upstream end 14of installation 10, to a lower elevation discharge region 16.Installation 10 also includes a turbine runner 18 of the type comprisinga hub 20 having a longitudinal axis 22, and a plurality of runner blades24 pivotally connected to hub 20. Each blade 24 is movable about arotational axis 26 extending in a direction generally perpendicular tolongitudinal axis 22. While the present invention will be described withreference to turbine runner 18 in which longitudinal axis 22 is verticalas shown in FIG. 1, those skilled in the art will appreciate that thepresent invention is similarly applicable to turbines disposedhorizontally or at any position deviating from the horizontal orvertical, depending on the particular configuration of passageway 12.Furthermore, axes of rotation 26 could instead be inclined relative tolongitudinal axis 22 (as in “Deriaz” turbines) without in any waydeparting from the scope of the present invention.

Intermediate upstream end 14 and rotational axis 26 is disposed adischarge ring 27 which directs the flow of water from upstream end 14toward turbine runner 18. Installation 10 includes a plurality of wicketgates 28, which may be adjusted in rotation to regulate the flow ofwater admitted to passageway 12, and stay vanes 30 which are designed tosupport the portion of installation 10 located above turbine 18, thatis, the thrust bearing 32, generator 34, and associated control systemsand components typically located in the power station, some of thesesystems constituting what is commonly known in the industry as the“governor”.

Referring now more particularly to FIGS. 6-11, hub 20 comprises anupstream region 36 and a downstream region 38 located on the upstreamand downstream sides of rotational axis 26, respectively. Turbine runner18 also typically includes between 2 and 9 runner blades 24. However, inmost of the Figures only one blade will be represented to facilitate thedescription of the present invention.

Each blade 24 comprises a hydrofoil generally designated as 40 having aninner surface 42 and a distal outer surface 44, a leading edge 46 and atrailing edge 48 separated from leading edge 46 by a water directingsurface 50 which comprises oppositely facing pressure and suction sides.For hydraulic considerations, hydrofoil 40 will usually be twisted asshown in FIG. 2 or 7. As a result, water directing surface 50 can becharacterized as having an inner portion 51, extending from innersurface 42, merging into an outer portion 53 extending to outer surface44.

Blade 24 is disposed for rotational movement relative to hub 20 with itsinner surface 42 spaced from the outer surface 52 of hub 20 byfunctional clearance δ. As more particularly shown in FIG. 18, hub 20 isgenerally hollow, the hollow cavity 54 being defined by an inner surface56 which is spaced apart and oppositely faces outer surface 52. As willbe explained below, cavity 54 conveniently houses the variousmechanisms, linkages and other systems necessary for the rotation ofblades 24 about axes 26. When blade 24 is at minimum pitch position(shown in FIG. 7), outer portion 53 of water directing surface 50 formsa significant impediment to the water flowing through passageway 12.Toward maximum pitch position (as illustrated in FIG. 8), inner portion51 of water directing surface 50 points in a direction generallyparallel to longitudinal axis 22. In other words, blade 24 is “flatter”at minimum pitch position than it is at maximum pitch position.

In a first embodiment of the present invention, outer surface 52 of hub20 swept by inner surfaces 42 of blades 24 during rotation of blades 24from maximum to minimum pitch is spherically shaped forming a sphericalfrustum comprising an upstream region 36 and a downstream region 38.Comparing FIG. 6 to a prior art hub illustrated in FIG. 4, it can bereadily appreciated that the included angle θ formed between the tworadiating lines R is substantially greater in the case of the presentinvention than in prior art hubs. Typically, in this first embodiment ofthe present invention angle θ will be at least 15% larger.

Because the blade inner surfaces 42 are also spherically shaped andconform to hub outer surface 52, inner surfaces 42 will substantiallyconform to outer surface 52 over the entire range of blade positions,including at minimum pitch position, thereby limiting the gap 58 formedtherebetween. As illustrated in FIGS. 9A and 9B, over the entire rangeof blade positions gap 58 remains substantially equal to functionalclearance δ. Such an improved spherically-shaped hub thereforeeliminates the large, essentially wedge-shaped gaps 60 typically formedbetween the hub and blades at blade pitch position other than maximumpitch position, as illustrated in FIGS. 3 and 5A which depict prior arthub configurations. Accordingly, as discussed earlier, the absence oflarge gaps 60 therefore reduces cavitation and flow disturbance, andimproves turbine efficiency and fish survivability.

Typically, a blade inner surface 42 meets a water directing surface 50along a relatively sharp edge. However, it is well known that sharpedges formed on runner blades create highly turbulent flows in regionsof the water flow proximate such edges. Accordingly, the presentinventors have also noted that in certain cases it may be possible tofurther improve some of these turbine parameters, and particularly thesurvivability of fish passing through turbine runner 18. Toward thatend, the sharp edges of the juncture of inner surface 42 with innerportion 51 of water directing surface 50, at least in the region ofleading edge 46, may be removed or softened as required depending on theextent of the overhang of the blade relative to the hub, or on the sizeof the gap formed between the blade and the hub. Such “rounded”configuration will typically reduce injury to the fish stricken by blade24 during rotation of hub 20, and will further reduce flow disturbancesin the region of such rounded edges.

Turning now to another embodiment of the present invention and referringmore particularly to FIGS. 12-16, it has been found by the inventorsthat it is possible to reduce cavitation in Kaplan turbines and improvethe efficiency of such turbine installations, while in both cases alsoimproving the survivability of fish as they pass through the turbine, byfurther preventing water from flowing into gap 58. To that end, a secondembodiment of the present invention includes a seal 62 attached to innersurface 42 of blade 24. Seal 62 projecting from inner surface 42 by apredetermined distance d₁, d₂, or d₃ depending on the size of gap 58(see FIGS. 14-16), will effectively be in contact with outer surface 52of hub 20 in upstream and/or downstream regions 36, 38, respectively,that are swept by blades 24 as they rotate about rotational axes 26.

Referring more particularly to FIGS. 14-16, seal 62 will be made of acorrosion-resistant or preferably corrosion-proof material (both beinghereinafter generically referred to as corrosion-resistant materials)such as an elastomeric material, or an elastomeric material coated witha friction reducing material such as teflon. Seal 62 may also be made ofa metal such as bronze (e.g., aluminum bronze), preferably forming agalling resistant combination with the material from which hub surface52 is made. Seal 62, which is advantageously removably attached to innersurface 42 to facilitate its replacement after extended use or in theevent it becomes damaged, can have one of several configurations. It canbe formed as a continuous strip extending from the region of the axis ofrotation of the blade to the leading or trailing edge of the blade.Instead, seal 62 may consist of a plurality of discrete strip portions.

Whether formed as a continuous strip or discrete sections, seal 62 canbe attached to blade 24 in various ways. For example, as illustrated inFIG. 14, seal 62 which extends from inner surface 42 by a distance d₁comprises a first portion 64 made of corrosion-resistant material andhaving a recess 66 configured to receive a fastener 68. Fastener 68cooperates with a non-pliable insert 70 designed to evenly distributethe force applied by fastener 68 to retain first portion 64 into amating recess 72 formed in inner surface 42. Seal 62 further includes aplug 74 made also of corrosion-resistant material filling cavity 66 andterminating at a point lying substantially at a distance d₁ from innersurface 42.

Alternatively and referring now to FIG. 15, seal 62 which extends frominner surface 42 by a distance d₂ may comprise a support portion 76 madeof elastomeric material and disposed below a second portion 78 which ismade of a corrosion-resistant material such as bronze or aluminumbronze. Seal 62 is removably attached to blade 24 by a suitably shapedretainer 80 cooperating with a fastener 82. If required, seal 62 mayalso include a non-pliable insert 84 to evenly support portion 76.

A third embodiment of seal 62 is represented in FIG. 16 in which seal 62extends from inner surface 42 by a distance d₃. In that case, thecorrosion-resistant portion of seal 62 is configured as a truncatedpyramid 86 received in a dove-tail groove 87 and supported by anon-pliable insert 88. Pyramid 86 is removably attached to blade 24 by asuitably shaped retainer 90 cooperating with a fastener 92.Alternatively and as shown in FIG. 16A, truncated pyramid 86 may includea cavity 91 to permit pyramid 86 to be squeezed for installation intogroove 87. Once installed in the groove, cavity 91 is then filled with acurable liquid compound such as an elastomeric material to preventpyramid 86 from become dislodged from groove 87. To permit removal ofthe seal when desired, groove 87 is advantageously provided proximatethe blade leading and trailing edges 46, 48, as applicable, with aretainer such an expandable locking device designed to prevent slidablemovement of pyramid 86 out of groove 87.

While any of the foregoing embodiments suitably prevents water fromflowing into gap 58, in certain cases it may be possible to optimizethis novel technique. For example, design considerations may permitreducing the length of gap 58, i.e., the distance separating the regionof the axis of rotation of the blade from the leading or trailing edgeof the blade. This can be achieved by enlarging palm 93 of blade 24 asshown in FIG. 13, and consequently the effective length of seal 62 canbe decreased. Other considerations may lead to a reduction of the sizeof gaps 94 formed between the outer surface of the blades and thedischarge ring. In those cases, another embodiment of the presentinvention may be used and will now be discussed referring moreparticularly to FIGS. 17 and 22.

Turbine installation 10 shown in FIG. 17 includes a discharge ring 27disposed in a region of passageway 12 substantially facing the bladesrotational axes 26. However, it has been recognized in the art ofhydropower generation that gaps formed between outer surface 44 and face96 upstream of blade rotational axis 26 are detrimental to the operationand environmental impact of the turbine. To address this shortcoming, asillustrated in FIG. 17 wherein to facilitate this explanation dischargering 27 is shown in cross-section and the blades and hub are shown threedimensionally, discharge ring 27 may have a substantiallyspherically-shaped face 96 oppositely facing and swept by outer surfaces44 of blades 24. As a result, outer surfaces 44 substantially conform toface 96 as blades 24 are rotated about axes 26 preferably over theentire range of rotation of blades 24, and as turbine runner 18 rotatesabout longitudinal axis 22.

While it is preferable for outer surface 44 and face 96 to conform overthe entire area swept by outer faces 44 both upstream and downstream ofaxis 26, in certain cases to achieve specified design and operatingcharacteristics it may be sufficient to have a portion only of outersurface 44 conform to face 96. For example, it may be sufficient forface 96 to be spherically-shaped only over an area 96 a extendingupstream of axis 26 instead of having face 96 (i.e., areas 96 a and 96b) substantially conform to outer surface 44. Alternatively, it may beacceptable for face 96 to be spherically-shaped only over an area 96 bextending downstream of axis 26. Furthermore, it may also be acceptablefor face 96 to be frusto-spherical, i.e., for selected portions only ofareas 96 a and/or 96 b to be spherically-shaped. This configuration maycause a portion of outer surface 44 to extend beyond (in other words tooverhang) spherically-shaped face 96, in the region of leading edge 46and/or trailing edge 48, at certain pitch positions of the blades. Wewill now turn to FIG. 22 to discuss how these various discharge ringconfigurations affect the gap formed therebetween as the blade rotatesabout axis 26.

FIG. 22 is a graphical representation at maximum blade tilt of thenormalized variation of the radial clearance i.e., of the gap betweenthe blade outer surface and the face of the discharge ring, for ablade/discharge ring combination of the present invention and two priorart blade/discharge ring configurations. In accordance with this otherembodiment of the present invention, gap 94 is substantially equal tothe functional clearance required between outer surface 44 and face 96to permit blade tilting. In addition and significantly, the presentembodiment causes gap 94 to remain essentially constant and equal tosuch functional clearance for all points along outer surface 44 upstreamand downstream of rotational axis 26.

Because discharge ring 27 has an annular structure, face 96 closelyconform with inner surfaces 44 all around discharge ring 27. In such anembodiment of the present invention, leakage losses are materiallyreduced as gaps 58 and 94 are minimized by the cooperation of oppositelyfacing spherically-shaped surfaces, specifically, by the closeconformance of blade inner surface 42 with hub outer surface 52, andblade outer surface 44 with discharge ring face 96. This will result inreduced cavitation, reduced injury to fish passing through the turbine,and improved efficiency of the turbine installation.

In certain cases, space inside the hollow hub becomes a dominantconsideration. A further embodiment of the present invention addressingsuch a situation will now be discussed referring more particularly toFIGS. 18-20. In that case, a linkage mechanism generally designated as100 is received in hollow hub 20 and connects blades 24 to a drivemechanism 102 (not shown) for rotation of blades 24 about rotationalaxes 26. Drive mechanism 102 may consist of one or several servo-motors,hydraulic cylinder(s), or hydraulic motor(s). Drive mechanism 102 isconnected to a piston head 104 to which linkage mechanisms 100 areremovably connected. In response to an appropriate command sent to drivemechanism 102, piston head 104 is displaced within chamber 106, therebycausing rotation of blades 24 about axes 26.

As more particularly illustrated in FIG. 18, linkage mechanism 100 has alongitudinal axis 107 which forms an included angle with hub axis 22.This “angled” configuration is used in certain cases to accommodate thenecessary longitudinal displacement of piston head 104 even thoughupstream and downstream regions 36, 38, respectively, arespherically-shaped. Linkage 100 preferably includes spherical jointsgenerally designated as 108 thereby facilitating translating movement ofpiston head 104 into rotational movement of blades 24. In particular,joints 108 include a pair spherically-shaped bearing portion 110disposed intermediate a pair of links 112 joining head 104 to bladetrunnion generally designated as 114. Additional considerations that maylead to the selection of an angled linkage mechanism include arelatively small hub diameter compared to the blade periphery diameter,the number of blades which as that number increases reduces the sweep ofeach blade, or the location of servomotors or other components necessaryto position the blades.

It is well known that the use of turbines with adjustable blades permitshigh efficiency output under a wide range of operating conditions, andin particular under various “net head” conditions, i.e., underconditions where the difference between the upper elevation source andlower elevation discharge region water levels varies widely. Such broadrange of operating conditions typically requires automatic andsimultaneous adjustment of blades 24 and wicket gates 28 in accordancewith load demand. However, to allow a turbine configured with reducedgaps between the hub and the inner surface of the blades and between theouter surface of the blades and the discharge ring as herein disclosedto maintain its improved cavitation, efficiency, and fish survivabilitycharacteristics over this broad range, the turbine will beadvantageously associated with control systems providing traditionalgovernor functions and control routines.

Typically, to adjust the position of the blades and wicket gates it isnecessary to sense various parameters including turbine speed, wicketgate position, blade pitch, net head, and output power, as the mostcharacteristic ones. In the early years of Kaplan turbines, sensing ofmost of these parameters was done mechanically, as explained inco-pending U.S. patent application Ser. No. 08/623,245, filed Mar. 28,1996 (now U.S. Pat. No. 5,947,679, issued Sep. 7, 1999)—after “1996”.which is incorporated herein by reference.

Thus, and referring back to FIG. 1, a control system generallydesignated as 120 may advantageously be used with the variousembodiments of the present invention. Control system 120 includes aplurality of sensors 122 designed to measure turbine operation and otherrelated control parameters. The electric signals generated by sensors122 are sent to a controller 124, preferably via signal conditioningcircuits (not shown). For example, the electrical signal representativeof the speed of turbine 18 is provided by a toothed disc mounted on theshaft of turbine 18; the disc is associated with two inductive sensingelements providing two independent signals to controller 120. Controller124 may also receive an electrical signal representative of the positionof wicket gate 28. Controller 124 preferably includes a digital-basedprocessor and required analog to digital conversion and signal scalingcircuits.

The information provided by the various sensors is then used in controlalgorithms allowing controller 124 to compute and generate variouscontrol signals, as required, for the efficient operation ofinstallation 10, without significantly compromising the gains in thefish survivability, cavitation, and efficiency achieved by theembodiment(s) of the present invention that is (are) associated withcontrol system 120. The control signals generated by controller 124 arethen fed to a plurality of signal converters generally designated as126. Signals from each signal converter 126 are sent in the appropriateform to associated actuators 128 (typically of the hydraulic-type), usedto adjust the position of blades 24 and the opening of wicket gates 28,as calculated by controller 124, for efficient operation of turbineinstallation 10. As a result, control system 120 provides another way,whether used alone or in combination with some of the other embodimentsof the present invention, to increase fish survivability, whileincreasing efficiency and reducing cavitation, of an installation havinga turbine of the type disclosed and claimed in this application.

Turning now to a further embodiment of the present invention andreferring to FIGS. 6 and 21, at times certain design considerations willnot permit increasing included angle 8 formed between the two radiatinglines R. In other words, it will not be possible to increase upstreamand/or downstream portions 36, 38 of hub 20 to an extent sufficient toensure that hub surface 52 swept by inner surface 42 is spherical.Accordingly, spherical hubs described in the foregoing may also beconveniently associated with blades of reduced chordal distance in thearea of the root of the blade, i.e., in the region of the bladeproximate the blade inner surface. However, if reducing the chordaldistance of a contemplated blade design decreases undesirable gapsformed between the blades and the hub, such approach also typicallyreduces the effective water directing surface of the blade. As a result,to return the effectiveness of the turbine design to its originaldesired value, this approach may require an increase in the number ofblades of the runner.

In particular and as illustrated in FIG. 6, blade 24 is characterized byan upstream chordal distribution 130 and a downstream chordaldistribution 132. In upstream distribution 130, the upstream chord 134,i.e., the distance taken along a perpendicular line extending fromrotational axis 26 to leading edge 46 varies from outer surface 44 toinner surface 42. Similarly, in downstream distribution 132, downstreamchord 136 separating axis 26 from trailing edge 48 varies from outersurface 44 to inner surface 42. Therefore, in cases where designconsiderations will not permit increasing included angle θ, another wayto ensure that gaps are not formed as blades 24 depart from maximumpitch position is to have blades 24 formed with leading edge 46extending toward blade rotational axis 26. This configuration isachieved by shortening upstream chord 134 in a root region 138 of blade24, as shown in FIG. 21.

The effect of shortening chordal distribution 130 in root region 138 canbest be understood by referring to FIG. 6 in which is shown a line 140radiating from the hub center through the juncture 142 of leading edge46 and inner surface 42, and continuing away from inner surface 42 tointersect leading edge 46 at a forward point 144. In other words, byextending leading edge 46 toward rotational axis 26 an area 148 isformed, area 148 being bounded by a portion of leading edge 46 extendingbetween points 142 and 144, and by line 140. As can be readilyappreciated, were leading edge 46 not extending toward axis 26 (as inprior art cases), line 140 would intersect leading edge 46 at only onepoint, i.e., at point 142. Conversely, the more significant the chordalreduction in root region 138 the larger area 148 will become.

Similarly, and as shown in FIG. 21, blade 24 may instead or also includea shortened downstream chord 136 in root region 138, thereby causingtrailing edge 48 to extend toward rotational axis 26. In such cases, andwithout illustrating this similar downstream construction in theFigures, a radiating line 140′ will intersect trailing edge 48 at points142′ and rearwardly at point 144′. In other words, by extending trailingedge 48 toward rotational axis 26 an area 148′ is formed, area 148′being bounded by a portion of trailing edge 48 extending between points142′ and 144′, and by line 140′.

As those skilled in the art will readily appreciate, shortening upstreamand/or downstream chordal distances in accordance with the presentinvention is not restricted to certain chordal dimensions, nor is itlimited to certain specific relative dimensional reductions of thesedistances. Accordingly and to facilitate a comparison of the chordaldistribution of a blade of the present invention to that of a prior artblade, one will note that in FIG. 21 the chordal distribution has beennormalized, both for the chordal distance and for the radial distancealong axis 26, i.e. for any point lying between outer surface 44 andinner surface 42.

As explained above, shortening upstream chord 134 and/or downstreamchord 136, in root region 138 causes blade inner surface 42 “to fallon”, i.e. to lie effectively in contact with, spherical hub outersurface 52 upstream, and/or downstream, of blade rotational axis 26. Asis apparent on FIG. 6, such blade configuration naturally enlarges aspace 150 formed between leading edge 42 and the region of hub 20 whereupstream region 36 meets the non-spherical portion 142 of hub 20.However and significantly, unlike gaps 60, enlarged space 150 will nottypically materially affect the operating characteristics of theturbine, nor will it increase the propensity of the turbine to injurefish because, for hydraulic considerations, leading edge 46 willnormally have a rounded profile as shown in FIG. 10.

Finally, according to yet another aspect of the present invention,spherical hubs and blades of the types described herein may alsoadvantageously be used as part of rehabilitation and other upgradeprojects to enhance certain operating characteristics of existingturbine installations. In such projects, one of the primary designconsiderations is to increase or at least maintain the total waterdirecting surface area of the turbine runner so as to increase (or atleast maintain) the ability of the blades to extract energy from theflow of water passing through the turbine. However, while reducing thechordal distribution in root region 138 of blade 24 effectively reducesgaps 58 and enhances certain operating characteristics of Kaplanturbines, as noted above, this approach also reduces the effective waterdirecting surface. Accordingly, in certain rehabilitation projects itmay be desirable to reconfigure turbine runner 18 by reducing thechordal distance in the root region of the blades, while increasing thenumber of blades to substantially maintain or preferably increase thepower extraction capacity of the turbine.

Specifically, in an existing turbine having M blades pivotally connectedto the hub, each blade comprising a water directing surface having aninner portion of a given chordal distance in a root region thereof. Toupgrade such turbine runner, it may be desirable to replace it with arunner having N improved blades. Each improved blade having an innerportion of a reduced chordal distance in a root region thereof. Tomaintain or preferably increase the power extraction capacity of theturbine, N is an integer at least equal to M times the ratio of thegiven chordal distance to the reduced chordal distance.

In light of the foregoing, it should be understood that the abovedescription is of preferred exemplary embodiments of the presentinvention, and that the invention is not limited to the specific formsdescribed. For example, those skilled in the art will readily appreciatethat blades 24 could have configurations other than those describedherein provided the inner and outer surfaces of the blades cooperatewith a spherically-shaped hub and/or discharge ring, respectively. Inaddition, seal 62 could be configured or attached to the blade in waysother than those described. Furthermore, controllers of the typeassociated with these improvements do not necessarily need to be of thedigital processor-based type. However, all of these other constructionsare, nevertheless, considered to be within the scope of this invention.Accordingly, these and any other substitutions, modifications, changesand omissions may be made in the design and arrangement of the elementsand in their method of operation as disclosed herein without departingfrom the scope of the appended claims.

What is claimed is:
 1. A turbine installation having reduced inner andouter gaps, the turbine comprising: a plurality of runner blades, eachblade comprising a hydrofoil being bounded by an inner surface and adistal outer surface, a leading edge and a trailing edge separated by awater directing surface, the blades being adjustable in pitch from amaximum pitch position in which an inner portion of the water directingsurface extends substantially in a direction of the water flow, to aminimum pitch position in which an outer portion of the water directingsurface is substantially perpendicular to the water flow; and a hollowhub having spaced apart inner and outer surfaces and a hub longitudinalaxis, each blade being pivotally connected to the hub about a rotationalaxis, the outer surface of the hub swept by the inner surfaces of theblades during rotation of the blades from the maximum pitch to theminimum pitch being spherically-shaped, and the inner surfaces of theblades substantially conforming to the outer surface of the hub, therebyreducing the inner gaps formed therebetween, wherein the turbine isdisposed in a water passageway extending from an upper elevation sourceof water to a lower elevation discharge region, the passagewaycomprising a discharge ring disposed in a region of the passagewaysubstantially facing the rotational axes of the blades, the ring havinga face oppositely facing the outer surfaces of the blades, the facebeing essentially frusto-spherically-shaped so that only a selectedportion of the face is spherically shaped to substantially conform tothe outer surfaces of the blades during rotation of the blades from themaximum pitch to the minimum pitch, thereby reducing the outer gapsformed therebetween.
 2. The turbine of claim 1, wherein the selectedportion of the face extends upstream of the blade rotational axis. 3.The turbine of claim 1, wherein the selected portion of the face extendsdownstream of the blade rotational axis.
 4. The turbine of claim 1,wherein at least one of the blades comprises a seal attached to theinner surface of the at least one of the blades downstream of the bladerotational axes, the seal being effectively in contact with the outersurface of the hub swept by the at least one of the blades as the bladesare rotated about their axes to further reduce the inner gaps.
 5. Theturbine of claim 1, wherein the selected portion of the facesubstantially conforms to a middle region of the outer surface of eachblade.
 6. A turbine disposed in a passageway through which water flowsfrom an upper elevation source to a lower elevation discharge region,the turbine having reduced inner and outer gaps, the turbine comprising:a hollow hub having spaced apart inner and outer surfaces and alongitudinal axis; a plurality of runner blades, each blade comprising ahydrofoil being bounded by an inner surface and a distal outer surface,a leading edge and a trailing edge separated by a water directingsurface, each blade being pivotally connected to the hub about arotational axis extending in a direction generally perpendicular to thelongitudinal axis so that its inner surface is proximate the hub, eachblade being rotatable from a maximum pitch position, in which an innerportion of the water directing surface extends substantially in adirection of the water flow, to a minimum pitch position in which anouter portion of the water directing surface is substantiallyperpendicular to the water flow, wherein the outer surface of the hubswept by the inner surfaces of the blades during rotation of the bladesbetween the maximum and minimum pitch positions is spherically-shaped,and wherein the inner surfaces of the blades substantially conform tothe outer surface of the hub, thereby reducing the inner gaps formedtherebetween; and a discharge ring disposed in a region of thepassageway proximate the rotational axes of the blades, the ring havinga face oppositely facing the outer surfaces of the blades, the facebeing essentially frusto-spherically-shaped so that only a selectedportion of the face is spherically shaped to substantially conform tothe outer surfaces of the blades during rotation of the blades about theblade axes between the maximum and minimum pitch positions, therebyreducing the outer gaps formed therebetween.
 7. The turbine of claim 6,wherein at least one of the blades has a seal attached to the innersurface of the at least one of the blades, the seal being effectively incontact with the outer surface of the hub swept by the at least one ofthe blades as the blades are rotated about their axes to further reducethe inner gaps.
 8. The turbine of claim 7, wherein the seal is removablyattached to the at least one of the blades.
 9. The turbine of claim 7,wherein the seal projects from the inner surface of the at least one ofthe blades by a predetermined distance.
 10. The turbine of claim 7,wherein the seal is made of corrosion-resistant material.
 11. Theturbine of claim 10, wherein the material is an elastomeric materialcoated with a friction reducing material.
 12. The turbine of claim 7,wherein the seal comprises a continuous strip disposed downstream of therotational axis of the at least one of the blades.
 13. The turbine ofclaim 6, wherein the selected portion of the face extends upstream ofthe rotational axes of the blades.
 14. The turbine of claim 6, whereinthe selected portion of the face extends downstream of the rotationalaxes of the blades.
 15. The turbine of claim 6, wherein the selectedportion of the face substantially conforms to a middle region of theouter surface of each blade.
 16. A turbine disposed in a passagewaythrough which water flows from an upper elevation source to a lowerelevation discharge region, the turbine having reduced inner and outergaps, the turbine comprising: a hollow hub having spaced apart inner andouter surfaces and a longitudinal axis; a plurality of runner blades,each blade comprising a hydrofoil being bounded by an inner surface anda distal outer surface, a leading edge and a trailing edge separated bya water directing surface, each blade being pivotally connected to thehub about a rotational axis extending in a direction generallyperpendicular to the longitudinal axis so that its inner surface isproximate the hub, each blade being rotatable from a maximum pitchposition, in which an inner portion of the water directing surfaceextends substantially in a direction of the water flow, to a minimumpitch position in which an outer portion of the water directing surfaceis substantially perpendicular to the water flow, wherein the outersurface of the hub swept by the inner surfaces of the blades duringrotation of the blades between the maximum and minimum pitch positionsis spherically-shaped, and wherein each blade has a chordal distancedefined by a distance taken along a perpendicular line extending fromthe rotational axis to the trailing edge, the chordal distance of eachof the blades being shortened in a root region of the trailing edgeproximate the hub so that a line extending from a center point of thehub to a junction of the inner and trailing edges of each bladeintersects the trailing edge at a location spaced outwardly from thejunction, thereby reducing the size of the spherical portion of the hubswept by the inner surfaces of the blades downstream of the rotationalaxes of the blades; and a discharge ring disposed in a region of thepassageway proximate the rotational axes of the blades, the ring havinga face oppositely facing the outer surfaces of the blades, at least aportion of the face being essentially spherically-shaped tosubstantially conform to the outer surfaces of the blades duringrotation of the blades about the blade axes between the maximum andminimum pitch positions, thereby reducing the outer gaps formedtherebetween.
 17. The turbine of claim 16, wherein the chordal distanceof each of the blades is shortened in the root region of the leadingedge proximate the hub, thereby further reducing the size of the portionof the hub swept by the inner edges of the blades upstream of therotational axes of the blades.
 18. A turbine installation having reducedinner and outer gaps, comprising: a water passageway extending from anupper elevation source of water to a lower elevation discharge region,the water passageway being formed at least in part by a discharge ring;a turbine runner disposed in the water passageway downstream of thedischarge ring, the turbine runner including, a hollow hub having spacedapart inner and outer surfaces and a longitudinal axis, and a pluralityof runner blades, each blade comprising a hydrofoil having an inner edgeand a distal outer edge, a leading edge and a trailing edge separated bya water directing surface, each blade being pivotally connected to thehub about a rotational axis extending in a direction generallyperpendicular to the longitudinal axis so that its inner edge isproximate the hub, each blade being rotatable from a maximum pitchposition, in which the water directing surface is substantially parallelto the longitudinal axis, to a minimum pitch position in which the waterdirecting surface is substantially perpendicular to the longitudinalaxis, wherein the outer surface of the hub swept by the blades has aspherical configuration downstream of the rotational axes of the bladesso that so that the inner edge of each of the blades proximate the bladetrailing edge closely conforms to the outer surface of the hub as theblades are rotated about their rotational axes to reduce the inner gapformed between the inner edge of each of the blades and the hub; andwherein the discharge ring has an inner surface facing the outer edgesof the blades, the inner surface of the discharge ring upstream of therotational axes of the blades being frusto-spherically-shaped so thatonly a selected portion thereof is spherically cooperable with the outeredge of each of the blades proximate the blade leading edge as theblades are rotated about their rotational axes to reduce the outer gapformed between the outer edge of each of the blades and the passageway.19. The turbine installation of claim 18, wherein the sphericalconfiguration of the outer surface of the hub swept by the bladesextends upstream of the rotational axes of the blades so that so thatthe inner edge of each of the blades proximate the blade leading edgeclosely conforms to the outer surface of the hub as the blades arerotated about their rotational axes to further reduce the inner gapformed between the inner edge of each of the blades and the hub.
 20. Theturbine installation of claim 18, wherein the inner surface of thedischarge ring downstream of the rotational axes of the blades isfrusto-spherically-shaped so that only a selected portion thereof isspherically cooperable with the outer edge of each of the bladesproximate the blade trailing edge as the blades are rotated about theirrotational axes to further reduce the outer gap formed therebetween. 21.The turbine installation of claim 17, further comprising an electricalclosed-loop control system for adjusting each blade in position betweenthe maximum and minimum pitch positions.
 22. The turbine installation ofclaim 18, further comprising a linkage mechanism received in the hollowhub and connecting the blades to a drive mechanism for rotation of theblades about the rotational axes, the linkage mechanism having alongitudinal axis disposed at an angle relative to the hub longitudinalaxis.
 23. A turbine installation having reduced inner and outer gaps,comprising: a water passageway extending from an upper elevation sourceof water to a lower elevation discharge region, the water passagewaybeing formed at least in part by a discharge ring; a turbine runnerdisposed in the water passageway downstream of the discharge ring, theturbine runner including, a hollow hub having spaced apart inner andouter surfaces and a longitudinal axis, and a plurality of runnerblades. each blade comprising a hydrofoil having an inner edge and adistal outer edge, a leading edge and a trailing edge separated by awater directing surface, each blade being pivotally connected to the hubabout a rotational axis extending in a direction generally perpendicularto the longitudinal axis so that its inner edge is proximate the hub,each blade being rotatable from a maximum pitch position, in which thewater directing surface is substantially parallel to the longitudinalaxis, to a minimum pitch position in which the water directing surfaceis substantially perpendicular to the longitudinal axis, wherein theouter surface of the hub swept by the blades has a sphericalconfiguration downstream of the rotational axes of the blades so that sothat the inner edge of each of the blades proximate the blade trailingedge closely conforms to the outer surface of the hub as the blades arerotated about their rotational axes to reduce the inner gap formedbetween the inner edge of each of the blades and the hub, and whereineach blade has a chordal distance defined by a distance taken along aperpendicular line extending from the rotational axis to the leadingedge, the chordal distance of each of the blades being shortened in aroot region of the leading edge proximate the hub so that a lineextending from a center point of the hub to a junction of the inner andleading edges of each blade intersects the leading edge at a locationspaced outwardly of the junction, thereby reducing the size of aspherical portion of the hub swept by the inner edges of the bladesupstream of the rotational axes of the blades; and wherein the dischargering has an inner surface facing the outer edges of the blades, theinner surface of the discharge ring upstream of the rotational axes ofthe blades being spherically cooperable with the outer edge of each ofthe blades proximate the blade leading edge as the blades are rotatedabout their rotational axes to reduce the outer gap formed between theouter edge of each of the blades and the passageway.